The nicotinic acetylcholine receptor (nACh receptor) is a pentamer consisting of five subunits (α, β, γ, ε, or δ) in which these subunits are circularly arranged to constitute an ion channel having cation selectivity (Nature, 2003, vol. 423, pp. 949-955). With regard to the nACh receptor, it is known that there are a plurality of subtypes such as a muscle type (α1β1γδ), a ganglion type (α3β4), and a central nervous system (CNS) type (α7, α4β2). Binding of an endogenous ligand acetylcholine to the nACh receptor leads to opening of an ion channel, which plays an important role in the expression or regulation of various physiological functions such as muscle contraction, inflammation, synaptic transmission and plasticity.
An α7 nACh receptor out of CNS type nACh receptors is present primarily in the cerebral cortex and hippocampus, and is believed to be involved in higher brain functions such as memory and learning. In fact, an α7 nACh receptor agonist has been reported to have various pharmacological effects such as improvement of Alzheimer's disease or CIAS (International Journal of Molecular Sciences, 2012, vol. 13, pp. 2219-2238), improvement of negative symptoms of schizophrenia (The American Journal of Psychiatry, 2008, vol. 165, pp. 1040-1047), inhibition of inflammatory responses (British Journal of Pharmacology, 2007, vol. 151, pp. 915-929), and exhibition of analgesic effects (British Journal of pharmacology, 2012, vol. 167, pp. 421-435). Therefore, a compound stimulating the α7 nACh receptor is considered to be promising as an agent for preventing or treating a disease such as dementia, cognitive impairment, schizophrenia, Alzheimer's disease, CIAS, negative symptoms of schizophrenia, inflammatory diseases, or pain.
On the other hand, it is known that the α7 nACh receptor exhibits higher Ca2+ ion permeability and is readily susceptible to desensitization in response to agonist stimulation when compared with other nACh receptor subtypes (Neuron, 1990, vol. 5, pp. 847-856). Therefore, with respect to agonists, there is a possibility of problems associated with attenuation of drug efficacy due to desensitization.
A positive allosteric modulator (PAM) is a group of compounds which themselves have no agonist activity and have an effect of enhancing the intensity of signals transmitted to cells by a receptor. In recent years, drug discovery research on PAMs for an α7 nACh receptor has been energetically proceeding with the aim of improving cognitive impairment seen in Alzheimer's disease patients and schizophrenia patients. In fact, it has become apparent that a plurality of PAMs for an α7 nACh receptor have cognitive function improving effects in various preclinical cognitive models (Biochemical Pharmacology, 2007, vol. 74, pp. 1155-1163). From the foregoing, it can be expected that PAMs for an α7 nACh receptor will become a drug for preventing or treating dementia, cognitive impairment, schizophrenia, Alzheimer's disease, CIAS, negative symptoms of schizophrenia, inflammatory diseases, or pain.
Up to now, compounds controlling an α7 nACh receptor have been reported.
Patent Document 1 discloses that a compound represented by the following general formula or a pharmaceutically acceptable salt thereof is a modulator of an nACh receptor, and there is a description regarding use in the treatment of diseases associated with cholinergic neurons in the CNS or peripheral nervous system (PNS).

(For symbols in the formula, refer to Patent Document 1)
Patent Document 2 discloses that a compound represented by the following general formula or a pharmaceutically acceptable salt thereof is an α7 nACh receptor modulator, and there is a description regarding use in the treatment of pain, psychotic disorder, cognitive impairment, or Alzheimer's disease.

(In the formula, each of X, Y or Z is selected from CH and N. For the other symbols, refer to Patent Document 2)
Patent Document 3 discloses that a compound represented by the following general formula, an optical isomer, or acid addition salt thereof is a PAM of nACh receptors.

(In the formula, X is fluoro or chloro; and n is 0, 1 or 2. For the other symbols, refer to Patent Document 3)